Electrical evaporators in which the evaporation rate of a liquid formulation from a wick can be adjusted by varying the relative positions of a heating device and the wick are known.
For example, Spanish Utility Model No. 1 005 422 discloses an evaporator in which a heating device and a wick can be moved vertically relative to one another by means of a mechanical device, such as a screw/nut thread mechanism, in order to increase or decrease the heat intensity to which the wick is exposed. European Patent Publication No. 0 942 648, by contrast, discloses an evaporator in which a heating device remains stationary while a wick and bottle are displaced vertically in the direction of the longitudinal axis of the wick using a screw/nut thread mechanism, thereby increasing or reducing the overlap between the wick and the heating device. Another type of evaporator is disclosed in European Patent Publication No. 0 943 344. In that evaporator, a heating device is mounted on a plug, which can be moved toward or away from a wick. U.S. Patent Application Publication No. 2003/0138241 A1 (“the '241 publication”), which is incorporated herein by reference, discloses yet another type of evaporator having an adjuster for displacing the upper portion of a wick toward or away from a heating device in a direction substantially perpendicular to the longitudinal axis of the wick. Several perceived shortcomings of these adjustable evaporators are that they are difficult to adjust in discrete intervals and that repeatability of adjustment is difficult.
In addition, some types of plug-in appliances, particularly wick-based evaporators, must be used in an upright orientation in order to work properly. Because some electrical outlets are vertical (i.e., one socket is above another one), while other outlets are horizontal (i.e., side-by-side sockets), it is preferable for these appliances to have a rotatable plug, which permits the device to be used in both vertical and horizontal outlets. U.S. Pat. No. 5,647,053, which also is incorporated by reference herein, discloses a wick-based evaporator having a rotatable plug. One perceived shortcoming of the forgoing type of evaporator is that it is difficult to tell when the plug is in a proper position for use. Also, the forgoing evaporators have no provision for locking the plug in the use-positions.